1. Field of the Invention
The present invention relates to multilayer inductor-capacitor (LC) composite components including a coil unit and a capacitor unit, and more specifically relates to a multilayer LC composite component which includes a capacitor unit having a ground-side capacitor electrode and a signal-side capacitor electrode which oppose each other with an insulating layer therebetween, the ground-side capacitor electrode having an electrode-free area at a central region thereof and the signal-side capacitor electrode being electrically connected to the coil unit via the electrode-free area.
2. Description of the Related Art
FIGS. 9, 10, and 11 show a perspective view, an exploded perspective view, and an equivalent circuit diagram, respectively, of a multilayer LC noise filter as an example of a known multilayer LC composite component. This multilayer LC noise filter is a so-called T-type LC noise filter constructed by disposing a first external electrode 55a, a second external electrode 55b, and an external grounding electrode 56 on a device 54 including a first coil unit 51, a second coil unit 52, and a capacitor unit 53 including signal-side capacitor electrodes 63 and ground-side capacitor electrodes 65. The first external electrode 55a is electrically connected to a base end portion (IN-side end portion) 51a of the first coil unit 51, the second external electrode 55b is electrically connected to a base end portion (OUT-side end portion) 52a of the second coil unit 52, and the external grounding electrode 56 is electrically connected to the ground-side capacitor electrodes 65.
The manufacturing process of this multilayer LC composite component will be described below with reference to FIG. 12. First, magnetic ceramic green sheets 62 having internal electrodes (coil patterns) 61 which define the first coil unit 51, dielectric ceramic green sheets (dielectric layers) 64 having the signal-side capacitor electrodes 63 (see FIG. 13B) which define the capacitor unit 53, dielectric ceramic green sheets (dielectric layers) 66 having the ground-side capacitor electrodes 65 (see FIG. 13A) which are to be grounded, magnetic ceramic green sheets 68 having internal electrodes (coil patterns) 67 which define the second coil unit 52, and external layer sheets (not shown) are laminated and press-bonded. Then, the patterns (electrodes) are electrically connected to each other by via holes, and firing is performed under predetermined conditions. Lastly, as shown in FIG. 9, the first external electrode 55a, the second external electrode 55b, and the external grounding electrode 56 are formed.
The above-described conventional multilayer LC composite component suffers from problems in that the insulation resistance decreases because of cracks which occur in the device 54 along the surfaces of the ground-side capacitor electrodes 65 due to the following reasons:
(1) As shown in FIG. 13A, each of the ground-side capacitor electrodes 65 has an oblong rectangular shape in plan view with an electrode-free area 71 at the central region thereof, and is formed such that the main portion of the corresponding ceramic green sheet 66 is covered by the ground-side capacitor electrode 65. Therefore, sufficient bonding strength cannot be obtained between the surfaces of the ceramic green sheets 66 on which the ground-side capacitor electrodes 65 are formed and the adjacent ceramic green sheets 64.
(2) The main portions of the ground-side capacitor electrodes 65 are located at the inside of the internal electrodes (coil patterns) 61 and 67 disposed at both sides of the capacitor unit 53, and penetrating electrodes (via-hole electrodes) 70 (see FIG. 13A) extend through the dielectric ceramic green sheets 64 and 66 at the center thereof. Therefore, pressure cannot be applied effectively in a pressing step of the laminating process, and sufficient bonding strength cannot be obtained between the layers.
(3) The external grounding electrode 56, which is electrically connected to the ground-side capacitor electrodes 65, is disposed on the device 54 so as to completely surround the region where the capacitor unit 53 is disposed. Therefore, the device 54 receives a large thermal stress at the region where the capacitor unit 53 is disposed in the firing process or in the process of attaching the external electrodes by firing due to the difference in the degree of thermal expansion and contraction between the external grounding electrode 56 and the device 54.
Although the thermal stress applied to the device can be reduced to some extent by forming the external grounding electrode only at a portion of the device so that it does not completely surround the device, this does not satisfactorily solve the above-described problem.
In addition, similarly to the case of the ground-side capacitor electrodes 65, cracks also occur along the surfaces of the signal-side capacitor electrodes 63 due to thermal contraction in the firing process, and therefore the insulation resistance decreases, although this is not such a big problem since the area of the signal-side capacitor electrodes 63 is generally smaller than that of the ground-side capacitor electrodes 65 in the capacitor unit 53.
Accordingly, in order to solve the above-described problems, preferred embodiments of the present invention provide a high-reliability multilayer LC composite component in which separation between layers at the capacitor unit including the ground-side capacitor electrodes and the signal-side capacitor electrodes is prevented so that the insulation resistance does not decrease.
According to a first preferred embodiment of the present invention, a multilayer LC composite component includes a coil unit including a stack of coil conductors, two adjacent coil conductors being separated by an insulating layer and being electrically connected to each other, and a capacitor unit including a ground-side capacitor electrode and a signal-side capacitor electrode which oppose each other with an insulating layer disposed therebetween, the ground-side capacitor electrode having an electrode-free area at an approximately central region thereof and the signal-side capacitor electrode being electrically connected to the coil unit via the electrode-free area, wherein the ground-side capacitor electrode extends to at least two opposing sides of the insulating layer and has a cut portion which extends continuously from the electrode-free area.
As described above, the ground-side capacitor electrode has the electrode-free area at the approximately central region, and a penetrating electrode (via hole electrode) used for providing electrical connection to the signal-side capacitor electrode is disposed in the electrode-free area. By forming the cut portion (another electrode-free area) in the ground-side capacitor electrode such that the cut portion and the above-described electrode-free area are connected to each other, the area where the electrode is not formed in the insulating layer on which the ground-side capacitor electrode is formed can be increased, so that the bonding strength between the insulating layer and the adjacent layer can also be increased. Accordingly, cracks in the device along the surface of the ground-side capacitor electrode due to the thermal contraction in the firing process are effectively prevented and minimized. As a result, a highly reliable multilayer LC composite component in which the insulation resistance does not decrease can be obtained.
In addition, since the electrode-free area and the cut portion of the ground-side capacitor electrode are connected to each other on the insulating layer, the bonding strength between the insulating layer and the adjacent layer can also be further increased.
Furthermore, in the case in which the electrode is formed by the screen printing method using an electrode paste, the area of a continuous region where the electrode paste does not pass through a screen mask can be increased. Accordingly, bleeding can be reduced in the printing process, so that the pressure resistance and the insulation resistance of the product can be increased.
In addition, in the multilayer LC composite component of preferred embodiments of the present invention, the ground-side capacitor electrode may have line symmetry with respect to a direction that is substantially parallel to the two opposing sides of the insulating layer.
When the ground-side capacitor electrode has line symmetry with respect to a direction that is substantially parallel to the two opposing sides of the insulating layer to which the ground-side capacitor electrode extends, the area where the ground-side capacitor electrode is formed and the area where the electrode is not formed can be arranged in a balanced manner. Therefore, the surface of the insulating layer on which the ground-side capacitor electrode is formed can be reliably bonded to the adjacent layer. Accordingly, cracks along the surface of the ground-side capacitor electrode due to the thermal contraction in the firing process can be more reliably prevented and minimized. As a result, a highly reliable multilayer LC composite component in which the insulation resistance does not decrease can be obtained.
In addition, in the multilayer LC composite component of preferred embodiments of the present invention, the ground-side capacitor electrode may be divided by the cut portion.
When the ground-side capacitor electrode has a pattern such that it is divided by the cut portion, the area where the electrode is not formed in the insulating layer on which the ground-side capacitor electrode is formed can be further increased and be arranged efficiently. Accordingly, the bonding strength between the insulating layer and the adjacent layer can be further increased.
In addition, in the multilayer LC composite component of preferred embodiments of the present invention, the ground-side capacitor electrode may be divided into four sections by the cut portion, and two of the four sections extend to one of the two opposing sides of the dielectric layer and the other two of the four sections extend to the other one of the two opposing sides.
When the ground-side capacitor electrode is divided into four sections by the cut portion and two of the four sections extend to one of the two opposing sides of the insulating layer and the other two of the four sections extend to the other one of the two opposing sides, the area where the electrode is not formed in the insulating layer on which the ground-side capacitor electrode is formed can be further increased and be arranged more efficiently. Accordingly, the bonding strength between the insulating layer and the adjacent layer can be further increased, and the present invention can be more effectively applied.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attachxc3xa9 drawings.